The present invention relates to a sintered Fe alloy which may suitably be used as a material for forming a valve seat to be used for an internal combustion engine, and more specifically to the sintered Fe alloy as the material for forming the valve seat with a requirement of the internal combustion engine with high power and high rotation.
A valve seat has a conical surface portion to which a valve is abutted and is a component part of an internal combustion engine. The valve seat is formed by processing of a cylinder material or a head casting material and by fit of a ring formed beforehand. In either case, the valve seat is required to improve a thermal conductivity and a strength at a high temperature.
Hitherto, there has generally been used a sintered Fe alloy, as the material for forming the valve seat wherein the strength at a high temperature and the abrasion resistance thereof have been improved in order to solve the requirement described above. There have been known, for example, a sintered Fe alloy obtained in a manner that Co, Ni, Cr, W, Mo, V or the like is added to a base powder (powdery raw material) of Fe to make a mixed powder (green compact body) which is then press-formed and thereafter is sintered, and a sintered Fe alloy is obtained in a manner that a hard particle such as ferroalloy, carbide, intermetallic compound or the like is added to the base powder of Fe to make the mixed powder which is then press-formed and thereafter is sintered. Further, there has been known a sintered Fe alloy to which an infiltration treatment of Cu, Pb or the like is carried out for improving a thermal conductivity and a strength and for giving a self-lubricity.
However, the latest valve seat must endure hard conditions in comparison with a conventional valve seat, with the requirement of the latest internal combustion engine with high rotation and high power. Therefore, a higher abrasion resistance is required for the valve seat.
In case that infiltration treatment of Cu is carried out for improvement of the function of the combustion engine, there is a problem that the manufacturing cost of the valve seat becomes high for a reason described below; in the first place, a powdery alloy for forming the valve seat is sintered to form a green compact body, and in the final place, the green compact body is again put in a furnace with a Cu green compact body composing of a simple pressed powdery Cu or a pressed powdery Cu alloy to infiltrate the Cu component into the green compact body. Therefore, the process of forming Cu powder and the two heat treatments in the furnace must be done. In case that the infiltration treatment of Pb is carried out for improvement of the function of the combustion engine, there is a problem that the manufacturing cost of the valve seat becomes high because the infiltration treatment is needed in addition to the sintered treatment, and Pb may give a bad influence to the environment.